1. Field of the Invention
The present invention relates to a sulfonium compound, a photoacid generator, and a resist composition, and more particularly, to a sulfonium compound which has a photon yield that can be controlled by introducing absorbers that are different from each other to the cation region in one molecule, provides a compound having two acid sites respectively having an acid generator that is different from the other, thereby addressing the inconvenience of using a mixture of different photoacid generators, has excellent miscibility within a resist, and has improved miscibility with resists; a photoacid generator, and a resist composition.
2. Description of the Related Art
Semiconductor microprocessing technology utilizes lithographic processes, and in such lithographic processes, chemically amplified resist compositions are frequently used. Such a chemically amplified resist composition includes a photoacid generator which is a compound that generates acid when irradiated with light.
This photoacid generator generates acid when the photoacid generator absorbs light that is irradiated in the semiconductor patterning process.
In the case of an onium which is one of these photoacid generators, the onium is degraded to a cation form or a radical form when irradiated with light, and exists in a different molecular form, while an acid is generated at the anion side. Thus, diffusion of acid occurs on the resist film at the time of wafer baking after light irradiation.
A photoacid generator is capable of directly affecting the pattern characteristics of a resist, such as the resolution of the resist or the line edge roughness (LER), due to various characteristic factors such as an ability to absorb light, the acid generation efficiency, an ability to diffuse the generated acid, and the strength of acid of the anion.
Existing photoacid generators have a structure which can generate only one kind of acid per molecule, so that when a photoacid generator having characteristics such as both high diffusivity and low diffusivity and both high permeability and low permeability, is needed in order to obtain a high resolution, there is an inconvenience of using a mixture of photoacid generators. Furthermore, when photoacid generators are used in mixture, there is a problem that the photoacid generators cannot be uniformly mixed into the resist, and thereby a resist pattern having uniform characteristics may not be obtained.
As an example of the existing photoacid generator, Korean Patent Application No. 10-2006-00133676 (filed Jul. 2, 2007, by Sumitomo Chemical Co., Ltd.) discloses a compound represented by the following formula:
wherein in the above formula, X represents an alkylene group or a substituted alkylene group; Y represents a hydrocarbon group having 5 to 30 carbon atoms and containing one or more aromatic rings; Q1 and Q2 each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms; A+ represents an organic counterion; and n represents 0 or 1.
In another instance, Korean Patent Application No. 10-2007-0062926 (filed Jun. 18, 2007, by Shin-Etsu Chemical Co., Ltd.) discloses a compound represented by the following formula:RiCOOCH2CH2CF2CF2SO3-M+  [Chemical Formula]wherein in the above formula, R1 represents an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 15 carbon atoms, or a heteroaryl group having 4 to 15 carbon atoms; and M+ represents a lithium ion, a sodium ion, a potassium ion, an ammonium ion or a tetramethylammonium ion.
It is described in the patent application filed by Shin-Etsu Chemical that a sulfonic acid represented by the above formula can exhibit strong acidity, various substituents can be introduced to the acid, and the range of molecular design flexibility is large.
However, the constitution of the existing acid generators is complicated because an acid generator having high diffusivity and an acid generator having low diffusivity, and an acid generator having high permeability and an acid generator having low permeability should be used together as a mixture in order to obtain high resolution. Also, in the case of using a mixture of two or more photoacid generators in order to obtain a photoacid generator having contradictory characteristics such as described above, there is a problem that uniform miscibility in the resist may not be obtained.